Besides providing basic communication functions, a CDMA communication system provides new data application services, such as facsimiles, short message exchanges, Internet accessing, etc. The new data application may comprise wireless personal computers, mobile offices, electronic transfer accounts transmission, handset network browsing, email transmitting and receiving, and the like. The feature of these applications is the burst characteristic of services, that is, a large amount of data is transmitted in a short time period, and after that, only a few of the data or none of the data will be transmitted. For example, when a WWW page is clicked by a user to connect, a download request is transmitted, and one or more packet sequences are transmitted during a request procedure, and a large amount of data on a channel is required to be transmitted rapidly. When a document requested by the user has been downloaded, the document is read by the user for a certain time period, and less amount of the data is transmitted on the channel during this time period. For such type of services, if channels with certain bandwidth are assigned conventionally to such services, the requirement for rapidly transmitting the data cannot be satisfied during service bursts, and also channel resources are wasted when there are less data. An effective resolution is to multiplex channels based on features of services, and the complementary between a plurality of services is utilized to transmit a plurality of services on one channel. The current data rate of a channel is then monitored. If a current data rate of a channel is very large, and a channel bandwidth cannot satisfy the requirement for transmission, reassignment of the channel will be executed. When services are idle, a small bandwidth will be reassigned to the channel to enhance a utilization ratio of the channel.
A typical feature of a packet service procedure is shown in FIG. 1. A session procedure of a packet service is composed of several packet calls. Each packet call comprises a plurality of packet requests, and an arrival time exists between different packets. When a call of a packet arrives, arriving data is read by a user for a period of time (reading time), and a small amount of data exists on a channel during this time period. After completing the reading of the data, a packet call will again be issued. The procedure is cycled continuously in this manner until the end of the packet service.
CDMA is a spread spectrum communication technology. One of the advantages of CDMA is to support packet services having variable data transmission rates. In the case of CDMA, multiple access is implemented by assigning a pseudo random code, which has an excellent characteristic of self-correlation and weak correlation to each user. A pseudo random code is used to convert user's signals into wideband spread spectrum signals, and the wideband spread spectrum signals are converted by a receiver into the original wideband signals that use the same pseudo random code. In a CDMA system, orthogonal variable spread factor (OVSF) codes, which ensure the orthogonality between different physical channels, are used for a channel code, because their spread factors (SFs) are variable. Therefore, different spread factors can provide different data transmission rate. The smaller the SF, the larger the data transmission rate is provided. This characteristic of CDMA allows a CDMA system to rapidly satisfy a variety of or variations of data transmission rates by selecting different spread factor codes.
A code tree structure of an orthogonal variable spread factor (OVSF) is shown in FIG. 2. The spread spectrum factors of a CDMA system are implemented by code resource management. All of the spread spectrum factors exist in a code tree. A code near a root node corresponds to a higher data transmission rate. The sibling nodes of the tree, i.e., the codes having the same length in a spread spectrum factor, are orthogonal, and a parent code is not orthogonal with a child code. The codes that are assignable in a code tree should satisfy the following conditions:
1) no code has been assigned on a path from the code to the root node C1,1 of the code tree;
2) no code has been assigned in a child tree having the code as the root node.
For a lower data transmission rate channel, assigning a small spread spectrum factor code will cause many large spread spectrum factor codes unable to be assigned, and the number of codes, which can be used by the other users, is restricted. Thus, when assigning the codes, the codes having a large spread spectrum factor are retained as much as possible to satisfy the channel data transmission rate so as to retain more resources for the CDMA system.
Also, channel utilization can be increased by a method of multiplexing a plurality of services by a CDMA system on a physical channel. As shown in FIG. 3, the multiplex occurs before or after encoding internally or externally, after multiplexing the services and encoding the channels, the multi-service data are mapped onto a physical channel. If the entire data transmission rate excesses an upper limit of the data transmission rate of a single code, several physical channels can be assigned. For packet data, such as WWW browsing, FTP loading, and the like, two methods are used by CDMA for data transmission. The first is short data package data transmission, i.e. short data packets are applied directly onto a randomly accessed burst channel. This method is also referred to as common channel packet data transmission, which is adaptively used for infrequent short data packets. For transmitting large and frequent data packets on dedicated channels, a dedicated channel with a suitable spread factor is selected by the CDMA system based on a data transmission rate and a size of packet data. When the packet data bursts occur, the channel with large capacity is selected for data transmitting. Thus, for small or infrequent data packets, channel capacity is decreased to adapt the variation of the data transmission rate.
When a service request reaches a CDMA system, if the service can be multiplexed on the original channel, the physical channels are re-configured by the CDMA system. If the service cannot be multiplexed successfully on the original channel, a code resource management module is requested by the CDMA system for code resources. If a code resource request fails, the service will be rejected.
When the services are assigned by the above CDMA system, it is necessary to multiplex many types of services to increase channel utilization. In one aspect, when assigning the channels and configurations, the specific features of different services are different, and the service features of the same service of different users are also different. In another aspect, when configuring the channels, if the service feature of a specific service cannot be understood, it will cause the configuration to be blindness, resulting in that the channel resources are wasted and/or re-configured frequently, thereby significantly affecting the performances of the CDMA system.
One of the objectives of the present invention is to provide a method for enhancing the channel utilization of a CDMA system. The method assigns a channel bandwidth and a multiplexing method to enhance the channel utilization and reduce the number of re-configurations based on service features of different services of different users.